Sometimes a body cavity, such as an aneurysm, is located in a surgically remote, delicate, and torturously formed region, such as within the cerebral vasculature, that requires a specialized delivery system to navigate to the region and safely and reliably deliver a coil implant.
U.S. Pat. Nos. 5,122,136 and 5,423,829 describe some existing electrolytic delivery systems having a pusher attached to an implantable platinum coil by detachment segment that can be eroded by an electrolytic process. The coil is advanced by the pusher through a microcatheter to the desired target site within the vasculature and an electrical current is applied to the pusher at the detachment segment. The electrical current causes the electrolytic erosion of the detachment segment that results in the separation of the coil from the pusher and the release of the coil at the target site. It is believed that there are numerous drawbacks and disadvantages to such electrolytic systems. One disadvantage of this design is believed to be that the detachment segment must be positioned distally of microcatheter for release (i.e., the operator cannot “pre-release” the coil within microcatheter if desired). Another disadvantage is believed to be that these systems require electrical insulation and isolation of the detachment segment to reduce the release of metallic particles created during detachment, which may cause unwanted embolization downstream of the target site. Another disadvantage is believed to be that these systems require the practitioner to wait for an unknown amount of time, typically 10-180 seconds, until the implant coil is released, with the release monitored by feedback from a specialized system using complex electrical drivers. Yet another disadvantage is believed to be that these systems generate “false positives” quite often, at a rate of 3-10%, that falsely indicate that the coil has been released when in fact it has not. Further, as with any electrochemical reaction in solution, the system needs to be within ionic fluids to function, and it is believed that undesirable gases are formed at both the anode and the cathode. Additionally, it is believed that there are guide wire and delivery system size limitations because these systems require a constant flow of electrolytes such as saline through the microcatheter to hasten the detachment time of the coil. Because of this need for electrolytes, it is believed that the outer diameter of an electrolytic delivery system is optimized for saline flow rather than for considerations of coil deliverability, pushability, and force transfer of the pusher, and the suppleness of the distal end of the delivery system.
U.S. Pat. Nos. 6,063,100 and 6,607,538 describe hydraulic delivery systems having a pusher attached to an implantable platinum coil with a frictional fit between a pressure cuff on the distal end of the pusher and a cylindrical solid proximal end of the coil. The platinum coil is advanced through a microcatheter by the pusher into the target site. Hydraulic pressure is applied to the proximal end of the pusher, creating hydraulic pressure at the distal end of the pusher and causing the cylindrical solid proximal end of the coil to be pushed out of the pressure cuff to cause the separation of the coil from the pusher. One disadvantage of this design is believed to be that such systems require complex catheter construction and rigorous purging to avoid the delivery of air emboli. Even after purging, it is believed that some air emboli are usually left in the system and will be inevitably injected into the patient during the detachment process. Another disadvantage is believed to be that these systems are time consuming to use because of the preparation of the pusher and because of the filling and attachment of pressure syringes. These systems are believed to be less reliable than electrolytic systems and at times have either failed to release the coil or prematurely released the coil. Additionally, with this type of design, it is believed that the delivery system is optimally sized for hydraulic detachment, and not sized to facilitate coil delivery or the action of the pusher-coil interface. These delivery systems have generally hollow conduits designed for high hydraulic pressures and, as a result, are rigid. The coil-pusher interface, as well, is stiff because part of the proximal end of the coil is wedged tightly into the distal end of the pusher.
U.S. Pat. No. 5,234,437 describes a mechanical delivery system with a pusher that is attached to an implantable platinum coil by a threaded portion at the distal end of the pusher that screws into the inner winds of the coil. The coil is advanced by the pusher through a microcatheter into the target site. Once positioned, the operator twists the proximal end of the pusher a number of times to unscrew the distal end of the pusher from coil implant. A disadvantage of this design is believed to be that the system will not work well in highly tortuous anatomy due to the diminishing torque transmission of the pusher, that is, the body of the pusher itself twists with little or no rotation of the threaded portion. The unscrewing operation of the pusher is also believed to cause undesirable movement of the entire system that could cause misalignment with the target site and cause the coil to be positioned undesirously within the target vessel. Also, the screw design is believed to require the operator to hyper-extend the pusher beyond the tip of the microcatheter to effect release and is non-retrievable at that point.
U.S. Pat. No. 5,895,391 and U.S. Pat. Publ. No. 2006/0276823 describe mechanical delivery systems. U.S. Pat. No. 5,895,391 describes a mating member attached to a vaso-occlusive member that is held in an opening with an interference wire. The interference wire presses the mating member into an opening through the wall of a holding member. U.S. Pat. Publ. No. 2006/0276823 describes a mechanical interlocking mechanism with engagement member attached to a distal end of a pusher member and that extends through a retaining ring at a proximal end of an embolic device. A detachment member extends through an aperture at the distal end of the engagement member to lock the embolic device onto the pusher member.
Accordingly a need exists for an implant delivery system that is easier to use and more reliable than systems currently on the market and that requires fewer steps and faster detachment.
A further need exists for a technique for treating a vascular defect or lesion with platinum coils without creating metallic or gaseous particulates during the detachment process.
A further need exists for an implant delivery system that has increased reliability measured by fewer false positive detachments and fewer premature detachments.
A further need exists for a coil-to-pusher interface that is less rigid than those of existing systems.
A further need exists for an implant delivery system with superior pushability with a supple distal flexibility profile.